There is an increased awareness of the possibility of attacks on metropolitan areas using chemical, biological and radiological warfare agents. Researchers at Oak Ridge National Laboratory have developed a biosensor system to detect toxic agents in primary-source drinking water, such as disclosed in U.S. Pat. No. 6,569,384 to Greenbaum et al. through the analysis of fluorescence induction curves. FIGS. 1(b, d, f, and h) illustrate exposure fluorescence induction curves recorded every 5 minutes when exposed to different toxic agents and data collection for each curve is within 10 seconds, while FIGS. 1(a, c, e, and g) provide controls (no toxins).
In order to detect the existence of toxic agents, the traditional method is to measure the so-called “efficiency of PSII (photosystem II) photochemistry”,
      PSII    ⁢                  ⁢    efficiency    =                    F        max            -              F        s                    F      max      where Fs is the value at the stable time and Fmax is the maximum value of the fluorescence induction curve, as shown in FIG. 2. The PSII efficiency represents a simple induction curve-based calculation of the fluorescence signal “signature”, and significant deviations thereof indicate the potential presence of a toxic agent in the water.
Although PSII efficiency is generally effective in detecting the presence of toxic agents, it fails in some cases due to the non-significant photochemical yield presented by certain toxic agents. Moreover, it cannot classify between different agents or the same agent with different concentrations. In addition, using this parameter it can take as long as 60 minutes to arrive at a decision regarding detection of a contamination event. The classification of different agents with a shorter response time is of profound importance, such as to reduce response time to a contamination event. With the knowledge of the type of toxic agent, appropriate medicine and rescue strategies can be used in time to save lives as well as counter the terrorist attacks.
FIG. 3(a) compares the average PSII efficiencies of controlled induction curves and the curves obtained from water exposed to four different toxic agents, and FIG. 3(b) shows the average standard deviation of each toxic-agent-exposed signal to its corresponding control signal. It is observed that there is no deterministic pattern in the deviation of PSII efficiency between control and exposure signals to indicate the presence of a specific toxic agent.